Tuesday, December 17, 2013

New paper suggests land-use changes played a big role in global warming

A new paper published in Geophysical Research Letters finds man-made land cover change caused "global warming of 0.73 °C during the pre-industrial era, which is comparable to the ~0.8 °C warming during industrial times."

The globe has only recovered 0.7C since the end of the Little Ice Age in 1850, and if this paper is correct that land cover changes alone could account for 0.7C of global warming during the pre-industrial era, this would suggest that land-cover changes could have caused at least as much warming during the industrial era along with the exponential increase in population and development.

Surface albedo changes from anthropogenic land cover change (ALCC) represent the second-largest negative radiative forcing behind aerosol during the industrial era. Using a new reconstruction of ALCC during the Holocene era by Kaplan et al. [2011], we quantify the local and global temperature response induced by Holocene ALCC in the Community Climate System Model, version 4 (CCSM4). We find that Holocene ALCC cause a global cooling of 0.17 °C due to the biogeophysical effects of land-atmosphere exchange of momentum, moisture, radiative and heat fluxes. On the global scale, the biogeochemical effects of Holocene ALCC from carbon emissions dominate the biogeophysical effects by causing 0.9 °C global warming. The net effects of Holocene ALCC [anthropogenic land cover change] amount to a global warming of 0.73 °C during the pre-industrial era, which is comparable to the ~0.8 °C warming during industrial times. On local to regional scales, such as parts of Europe, North America and Asia, the biogeophysical effects of Holocene ALCC are significant and comparable to the biogeochemical effect.